Properties of lead zirconate-alumina ‘nanocomposites’

Microstructures, Vickers hardness and dielectric properties of PbZrO₃ ceramics with co-additions of 0.5-5 vol% Al₂O₃ nanoparticles have been investigated. The additive inhibited grain growth, with average grain size decreasing from ∼13 μm for PbZrO₃ to ∼1 μm for the nanocomposites. The mode of fracture also changed, from predominantly inter-granular in PbZrO₃ to a mixed-mode of intra- and inter-granular fracture in the composite samples. Vickers hardness values increased from 2.9 GPa for PbZrO₃ to 4.1 GPa for the sample with 1 vol% Al₂O₃, but there was a more gradual increase for higher Al₂O₃ contents. Plots of relative permittivity versus temperature indicated subtle differences which were attributed to a chemical reaction between the additive and matrix during sintering. X-ray powder diffraction showed that lead aluminium oxides were the principal products of this reaction.     

Effect of Sintering Temperature on Phase Transition and Mechanical Properties of Lead Zirconate Ceramics

Phase transition and mechanical properties of PbZrO₃ (PZ) at different sintering temperatures were studied. The Curie temperature depends on the sintering temperature. Hardness and fracture toughness of the PZ were measured using Vickers and Knoop microhardness testers. The lower density at the higher sintering temperature resulting from the loss of lead oxide (PbO) causes the lower value of the Curie temperature, hardness and fracture toughness. The results were well corresponding to the microstructure of the PZ ceramics.     

Improvement in dielectric and mechanical performance of CaCu<Subscript>3.1</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12.1</Subscript> by addition of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

The properties of CaCu_3.1Ti₄O_12.1 [CC3.1TO] ceramics with the addition of Al₂O₃ nanoparticles, prepared via a solid-state reaction technique, were investigated. The nanoparticle additive was found to inhibit grain growth with the average grain size decreasing from approximately 7.5 μm for CC3.1TO to approximately 2.0 μm for the unmodified samples, while the Knoop hardness value was found to improve with a maximum value of 9.8 GPa for the 1 vol.% Al₂O₃ sample. A very high dielectric constant > 60,000 with a low loss tangent (approximately 0.09) was observed for the 0.5 vol.% Al₂O₃ sample at 1 kHz and at room temperature. These data suggest that nanocomposites have a great potential for dielectric applications.     

Properties of hydroxyapatite/zirconium oxide nanocomposites

Effects of zirconium oxide (ZrO₂) nanoparticles additive on the microstructure and physical properties of hydroxyapatite (HA) were investigated. The HA powder was derived from natural bovine bone by a sequence of thermal processes. The composites containing nanoparticles of ZrO₂ (0.2–1.0 vol%) were fabricated by a solid-state reaction mixed oxide method. All samples showed traces of HA, beta-tricalcium phosphate (β-TCP) and alpha-tricalcium phosphate (α-TCP) phases while the x≥0.1 samples also showed ZrO₂ phase. Amount of β-TCP and α-TCP phases tend to decrease with ZrO₂. The additive inhibited grain growth as a result of a decrease in grain size. However, the x=0.2 sample exhibited higher hardness value which is consistent with the density data. In addition, bioactivity test suggested that the additive promoted an apatite forming with the values of Ca/P close to the value obtained from HA.     

Dielectric properties of strontium iron holmium niobate ceramics

Strontium iron holmium niobate (Sr(Fe_1?xHo_x)_0.5Nb_0.5O₃) ceramics were synthesized via a solid-state reaction technique. The undoped ceramic showed an orthorhombic phase, but it transformed to a pseudocubic phase for higher Ho concentrations. A low solubility limit of Ho in SFN caused a formation of second phase for the x=0.15 ceramic. Dielectric behavior of undoped ceramic exhibited high dielectric constant over a wide temperature range. However, the doping shifted this region to a higher temperature. The doping also shifted the peak of dielectric loss to a higher temperature. Activation energy of dielectric relaxation increased with increasing Ho concentration. In addition, complex impedance analysis was applied to determine the behaviors of grain boundary and grain after doping.     

Influence of Ca substitution on microstructure and electrical properties of Ba(Zr,Ti)O3 ceramics

In the present work, lead-free (Ba_1?xCa_x)(Zr_0.04Ti_0.96)O₃ (x=0.00–0.09) ceramics were fabricated via a solid-state reaction method. The microstructure and electrical properties of the ceramics were investigated. The microstructure of the BCZT ceramics showed a core shell structure at compositions of x=0.03 and 0.06. The substitution of small amount of Ba²⁺ by Ca²⁺ resulted in an improvement of the piezoelectric, dielectric and ferroelectric properties of the ceramics. The orthorhombic–tetragonal phase transition was found in the composition of x≤0.03. Piezoelectric coefficient of d₃₃～392 pC/N and lowest E_c～3.3 kV/cm with highest P_r～14.1 μC/cm² were obtained for the composition of x=0.03 while its Curie temperature (T_C) was as high as 125 °C. However, the ferroelectric to paraelectric transition temperature had slightly shifted towards room temperature with increasing Ca²⁺ concentration.     

Preparation and dielectric properties of (Sr1−xCax)Fe0.5Nb0.5O3; (x=0.0, 0.1, 0.2) ceramics

In the present work, strontium calcium iron niobate ((Sr_1?xCa_x)Fe_0.5Nb_0.5O₃; SCFN) (x=0, 0.1, and 0.2) powders were synthesized for the first time using a molten salt technique. The pure phase perovskite obtained at a relative low calcination temperature of 800 °C was characterized using the X-ray diffraction technique (XRD). SCFN ceramics were fabricated and their properties were investigated. The XRD data of the SCFN ceramics was consistent with an orthorhombic symmetry. However, the solubility of Ca in the SCFN ceramics had an upper limit at x=0.1. All ceramics showed a large dielectric constants. The Ca doping inhibited grain growth, but produced an improvement in dielectric–temperature stability. Furthermore, the doping reduced loss tangent, especially for the x=0.1 sample. These results suggest that the SCFN ceramics prepared from molten salt synthesis exhibit a good dielectric performances, compared to many high dielectric materials that have been prepared using the conventional method.     

The effect of heat treatment temperature on phase formation and luminescence properties of calcium magnesium silicate glass-ceramics doped with Sm2O3

Abstract

The transparent glasses of CaO-MgO-Al₂O₃-SiO₂-ZnO system doped with Sm₂O₃ was prepared by conventional melt-quenching method. The obtained glasses were heat treated at a suitable temperature (875?°C–920?°C for 2?h) identified by differential thermal analysis (DTA). Phase formation and microstructure of glass-ceramics were characterized by X-ray diffraction and scanning electron microscopy, respectively. The optical transmission spectra were recorded by UV-Vis spectrophotometer in the wavelength range between 350 and 1000?nm. It was found that the increase in heat treatment temperature reduced the transparency of the glass-ceramics. The luminescence properties were identified by fluorescence spectroscopy. The excitation spectra of Sm₂O₃ doped CaO-MgO-Al₂O₃-SiO₂-ZnO glass-ceramic samples are in wavelength range of 550–750?nm and the emission spectra exhibited a strong orange-red luminescence composed of 562, 599 and 654?nm under excited at 402?nm. The results of XRD studies revealed the occurrence of diopside (CaMgSi₂O₆) and akermanite (Ca₂MgSi₂O₇) phases. The increasing of heat treatment temperature has no effect on the shift of emission spectra.     

High magnetic and ferroelectric properties of BZT-LSM multiferroic composites at room temperature

In this research, the effects of La_0.7Sr_0.3MnO₃ additive on the phase evolution, microstructure, dielectric, ferroelectric and magnetic properties of BaZr_0.07Ti_0.93O₃ ceramics were systematically investigated. The (BaZr_0.07Ti_0.93O₃)/x(La_0.7Sr_0.3MnO₃) or BZT/xLSM (where x?=?0, 5, 10 and 20?mol%) ceramics were prepared via a solid state reaction method. A pure perovskite phase is observed for the samples of x?≤?10?mol%. The M-H hysteresis loops also show an improvement in the magnetic behavior for higher LSM content samples as well as the modified ferroelectric properties. However, the 5?mol% sample exhibited the optimum ferroelectric and ferromagnetic properties with remnant magnetization (M_r) and remanent polarization (P_r) of 2.38?emu/g and 10.5?µC/cm², respectively. The dielectric-temperature curves show that the two phase-transition temperatures as observed for the unmodified BZT ceramic merges into a single phase-transition temperature for the 5?mol% sample and then become flat curves for the 10?mol% sample. In addition, the mechanical properties i.e. Knoop hardness and Young's modulus values increase with increasing LSM content, where Knoop hardness and Young's modulus values for the 20?mol% sample are increased by ~ 45% and ~ 104%, respectively, as compared to the unmodified sample.